The invention pertains to a calendar stepping mechanism of an eternal calendar of a clock, the stepping mechanism having a stepping lever driven once per twenty-four hours around a pivot axis between a normal position and a raised position, a probe finger on the stepping lever, which can be moved radially from the outside against the circumferential periphery of a stepped month disk, the periphery being provided with twenty indentations of different depths and twenty elevations, which represent the forty-eight months of a leap year period, where the stepped month disk can be driven to rotate at a rate of one step per month and one revolution per four years, a rotatably supported calendar wheel having thirty-one teeth or a multiple thereof, where a stepping tooth, projecting beyond the other normal teeth, is provided for each set of thirty-one teeth, wherein the calendar wheel can be advanced by a pawl tooth of a stepping pawl, which is hinged to the stepping lever and can engage radially in the gaps between the teeth of the calendar wheel under the pivoting movement of the stepping lever, this movement depending on the contact position of the probe finger on the periphery of the stepped month disk, and wherein the clock's display of the calendar date can be driven by the calendar wheel.
Eternal calendars are mechanisms which allow a clockwork to step the calendar display forward in such a way that, on the correct day at the end of each month, the calendar display is set automatically to the first day of the new month under consideration of whether the year in question is a leap year or not. The information on the correct length of the various months is stored in a stepped month disk with indentations of different depths, which advances one step each month and completes one revolution every four years. This stepped month disk causes a stepping lever to perform a stroke corresponding to the length of the month in question, as a result of which, at the end of the month, it is possible all at once to step through the appropriate number of additional days required to display the first day of the new month. It is therefore necessary for the stepping lever both to advance the wheel one day forward every day and to advance the wheel one or more days forward at the end of the month to reach the point at which the new month begins.
In a calendar stepping mechanism of the type described above, it is known that the stepping lever has two shifting elements, one of which engages in the calendar wheel to step the date forward by one day. The calendar wheel carries a worm-like disk, which is oriented in such a way that, depending on the stroke determined by the stepped month disk, the second shifting element of the stepping lever engages in the step of the worm at the end of the month and advances the calendar wheel to the first day of the new month.
Because of the presence of two shifting elements, it is necessary to adjust their position with respect to the calendar wheel and with respect to each other with great precision to ensure the correct engagement at the correct moment. For the stepping operation at the end of the month, one shifting element must take over the stepping function from the other shifting element, which leads to jerks and changes in rotational speed and which must also be adjusted with great precision.